Offshore structures in the form of large offshore platforms are erected on the ocean floor for the purpose of drilling a large number of wells into the ocean floor in order to develop oil and/or gas fields. A platform may take the form of a rectangular structure with a plurality of legs extending from the ocean floor up to a point above the surface of the water where a platform is positioned on the top of the legs. In order to anchor the structure to the ocean floor and prevent its overturning, the structure is usually provided with a plurality of short skirt sleeves in the form of elongated cylindrical elements which may take the form of eight foot diameter pipes welded to the lower end of the platform and extending substantially parallel to the legs thereof. A smaller diameter tubular pile which may be, say, seven feet in diameter, is driven through the skirt sleeves as much as several hundred feet in the ocean floor. The pile above the skirt sleeve is cut off and the sleeve and pile are then cemented together.
The cementing of pile within the skirt sleeves may take many forms. In general, however, a common method is to have a cementing pipe, say, two inches in diameter, welded to each of the legs of the platform and extending from the top of the platform down to the lower end thereof where a lateral pipe is run to one or more of the closest pile sleeves which are outboard of the legs of the platform. After a pile has been driven through the skirt sleeve and cut off to the desired length, grout is pumped down the cement or grout line outside the leg and through the cross over lateral pipe which is in communication with the interior of the skirt sleeves. Since a smaller diameter pile is always used within a larger diameter skirt sleeve, and an annular space is formed between the pile and the sleeve which is filled with grout which is pumped down the two-inch grout line and into the annular space outside the pile. In waters up to 1,000 feet deep, divers may be sent down to inspect the operations or to open and close valves in the grout lines as needed. The use of divers in deeper waters is not generally feasible.
Another problem with the use of steel grout lines affixed to the legs of the platform is that in off-loading a platform from barges or hoisting it with a derrick barge, some of the grout lines may be damaged.